Aircraft and other passenger transportation vehicles are often equipped with vacuum toilets in the lavatories. Although efficient, vacuum toilets tend to have a rather loud flush sound. This can be disconcerting or annoying to passengers seated near the lavatory. It is also possible to provide galley sinks with vacuum flushing capabilities in order to allow the sinks to dispose of mixed waste. Accordingly, although the features disclosed herein are equally applicable to vacuum sinks as well as vacuum toilets, the description will refer to and focus on vacuum toilets, which are more common.
Current vacuum toilets typically inject rinse water at the beginning of the flush. This causes the waste to move down in the toilet bowl, close to the exit of the bowl, allowing the vacuum to remove the waste and transport it to a holding tank during a flush. The present inventors have also found that rinse water can help reduce the spike in sound levels when the flush valve opens and/or closes to vacuum, as well as during the steady state in between opening and closing.